Many industrial processes involve a combustion operation which results in formation of an effluent gas containing one or more by-product acidic compounds. Reducing the acidic gas content of the effluent gas prior to discharging the gas to the ambient air will reduce air pollution. In particular, reducing the SO2, SO3 and H2SO4 content of such effluent gases as these compounds can reduce unsightly gas plumes, reduce corrosive by-products, and reduce the risk of harmful human exposure. These problems may be particularly acute in coal-fired power plants which produce significant amounts of SO2 and/or SO3. Other industrial processes also involve formation of gaseous effluents that contain acidic gases including, for example, waste incinerators, sulfuric acid plants, non-coal fired power plants (e.g., oil), large-scale diesel generators, boilers, brick and ceramic furnaces, and lime and cement kilns.
Various flue gas desulfurization (“FGD”) processes have been developed to reduce the amount of acidic gases in the effluent gas and, in particular, to reduce the amount of SO2, SO3 and/or H2SO4. One such method involves introducing a dry alkaline sorbent such as hydrated lime (Ca(OH)2) or pulverized quicklime (CaO) into the exhaust duct through which the flue gas passes to react the sorbent with the acid compound to form a particulate solid (e.g., CaSO3 or CaSO4) which may be removed in a downstream ash collection system. Such methods and, in particular, methods which involve use of hydrated lime, may result in occlusion of processing equipment such as the outlet end of injectors (synonymously “lances”) which distribute hydrated lime into the exhaust duct. Occlusion of one or more injectors significantly reduces the effectiveness of the FGD system and requires that the system by intermittently shut-down to free the occlusion from the injectors.
A continuing need exists for methods for reducing the acidic gas content of effluent gases (e.g., flue gases produced from coal-fired power plants) which involve use of hydrated lime and/or pulverized quicklime and which reduce or even eliminate occlusion problems associated with such methods.